Recombination, decreased host specificity and increased mobility may have driven the emergence of maize streak virus as an agricultural pathogen

Abstract

Maize streak virus (MSV; family Geminiviridae, genus Mastrevirus), the causal agent of maize streak disease, ranks amongst the most serious biological threats to food security in subSaharan Africa. Although five distinct MSV strains have been currently described, only one of these – MSV-A – causes severe disease in maize. Due primarily to their not being an obvious threat to agriculture, very little is known about the ‘grass-adapted’ MSV strains, MSV-B, -C, -D and -E. Since comparing the genetic diversities, geographical distributions and natural host ranges of MSV-A with the other MSV strains could provide valuable information on the epidemiology, evolution and emergence of MSV-A, we carried out a phylogeographical analysis of MSVs found in uncultivated indigenous African grasses. Amongst the 83 new MSV genomes presented here, we report the discovery of six new MSV strains (MSV-F to -K). The non-random recombination breakpoint distributions detectable with these and other available mastrevirus sequences partially mirror those seen in begomoviruses, implying that the forces shaping these breakpoint patterns have been largely conserved since the earliest geminivirus ancestors. We present evidence that the ancestor of all MSV-A variants was the recombinant progeny of ancestral MSV-B and MSV-G/-F variants. While it remains unknown whether recombination influenced the emergence of MSV-A in maize, our discovery that MSV-A variants may both move between and become established in different regions of Africa with greater ease, and infect more grass species than other MSV strains, goes some way towards explaining why MSV-A is such a successful maize pathogen.

A genome-wide pairwise-identity-based proposal for the classification of viruses in the genus Mastrevirus (family Geminiviridae)

“…For example, suitable alternative names for MSV-A and MSV-B that reflect the different host preferences of viruses belonging to these strains would be MSV-Maize and MSVDigitaria, respectively [58]. Although a descriptive strain name could potentially be useful, it should be borne in mind that unless it genuinely reflects the characteristics of all members of a strain, it also could be quite misleading.…”

“…For example, whereas the ''A'' strain of MSV is clearly the only group of MSV variants that cause severe disease in maize [37,58], the ''A'' strain of WDV preferentially infects barley, whereas the ''C'' strain preferentially infects wheat [50].…”

A novel maize-infecting mastrevirus from La Réunion Island

“…Monocotinfecting mastreviruses have previously been found throughout Africa (including the South-west Indian Ocean islands: SWIO), Europe, Japan, Southeast Asia, the island of Vanuatu, and Australia. Mastreviruses previously found on SWIO islands such as La Réunion and Mauritius include various maize streak virus (MSV) strains, sugarcane streak Réunion virus (SSRV) and sugarcane streak virus (SSV) [13,19,25,26].…”

First genome analysis and molecular characterization of Chickpea chlorotic dwarf virus Egyptian isolate infecting squash

“…A great emphasis has been emerged here stressed on the biological difference between the viral isolates would be classified into different strains. For example, whereas the ''A'' strain of MSV is clearly the only group of MSV variants that cause severe disease in maize [28,42], the ''A'' strain of WDV favourably infects barley, whereas the ''C'' strain preferentially infects wheat [39], our Egyptian isolate of CpCDV could be assigned as a specific strain preferentially infects squash which is essentially a non-host species of this virus. Through recombination analysis performed using RDP4, it has been observed that the Egyptian isolate although more closely related to the Syrian isolate but a considerable part of the genome found to be originated from a different isolate of BeYDV assigned in the genbank under accession no ENA|DQ458791 (Fig.…”